Project Summary A new generation of optical and optogenetic tools is allowing rapid progress in our understanding of fundamental processes in the living brain and how these processes go awry in disease. One of the key technologies underlying in vivo imaging is 2-photon microscopy, which allows fluorescent material deep within the brain to be examined. In recent years, there have been major technological improvements in 2-photon imaging systems that allow for faster and deeper imaging. These new 2-photon imaging technologies allow qualitatively new types of studies. Resonant- scanning technology that permits imaging at 30Hz allows neuroscientists to study neural responses to single stimuli, on single trials, without averaging across time or trials. This 30Hz rate of acquisition is also faster than many of the movement artifacts that occur within the living brain, such as respiration and heart beats, allowing for artifact correction rather than blurring, and permits the study of sub- neuron features such as dendrites and dendritic spines. New laser technology and new optical tools allow the use of longer-wavelength indicators (such as red indicators), which can be stimulated and examined at much greater depths than the traditional shorter-wavelength indicators. In short, recent technological improvements have had a transformative impact on 2-photon imaging. This project will provide NIH-funded systems neuroscientists at Brandeis University with a sustainable, state-of-the-art in vivo 2-photon imaging station with accompanying instrumentation for animal anesthesia, physiological monitoring, visual stimulation, and behavioral monitoring of eye movements and movements on a treadmill. The clusters of instrumentation that will be assembled have been carefully selected for performing advanced brain imaging in the living brain while animals are anesthetized or are engaged in behaviors of interest. Currently, Brandeis has no in vivo resonant- scanning 2-photon microscope, and this shared instrumentation will be a game-changing improvement in our capabilities. The shared instrumentation will be placed in the middle of our systems neuroscience labs to allow for synergistic interactions among the users. Importantly, this equipment will immediately permit advances in our understanding of neural plasticity, neural development, visual perception, taste perception, navigation, and decision making.